Puck-based input device with rotation detection

ABSTRACT

The present invention includes a pointing device having a first surface on which a puck field of motion is defined, a moveable puck, and a position detector. The moveable puck is confined to move on the first surface within the puck field of motion. The position detector determines a position of the puck in the puck field of motion and an angle of rotation of the puck about an axis perpendicular to the first surface. In one embodiment, the puck includes a puck electrode on a second surface on the puck that is parallel to the first surface. The first surface includes first, second, and third electrodes that are parallel to the puck electrode, the puck electrode overlying a portion of each of the first, second, and third electrodes.

BACKGROUND OF THE INVENTION

Modern computer operating systems and graphics programs require apointing device for controlling the position of a cursor on the computerdisplay. Likewise, handheld devices such as personal informationmanagers and cell phones would also benefit from the inclusion of such apointing device. For desktop PCs, the most successful pointing device isthe “mouse”. A mouse is a hand held object that is moved over a flatsurface near the keyboard to control the motion of a cursor on thecomputer display. The direction and distance over which the mouse ismoved determines the direction and distance the cursor moves on thedisplay. A conventional mouse provides a rigid object that a user canmove with great precision. For a desktop computer, the mouse provides asatisfactory solution to the pointing problem. On the occasion when theworkspace is not large enough to provide a path over which the mouse canmove and accommodate a desired cursor movement on the screen, the usersimply picks up the mouse and recenters the mouse in the workspace.

In addition to providing the above-described pointing function, themouse has evolved to include additional buttons and wheels that are usedto provide other forms of input to the computer. For example, most mousedesigns now provide a second button for signaling an applicationspecific action such as displaying a menu from which the user can selectother functions. In addition, a scroll wheel is provided in manydesigns. The scroll wheel is used to scroll text on the screen orcontrol other multi-valued functions in specific applications. Forexample, the zoom level in many graphics programs can be increased ordecreased by rotating the scroll wheel.

While the mouse has provided a satisfactory solution to the pointingdevice problem in the desktop PC market, a similarly successful deviceis not available for portable and hand-held computers. These computersare often used in environments that lack a sufficiently large flatsurface near the keyboard over which a mouse can be moved. In addition,the need to carry a separate pointing device makes the mouse less thanideal for these applications. Hence, some other form of pointing deviceis needed when these computers are used in such environments.

A pointing device for use in these environments must solve the problemof moving a cursor quickly and accurately. In addition, the device mustoperate in an intuitive fashion that a novice user can comprehendwithout extensive instruction. In addition, the pointing device mustoperate in a limited workspace and fit within the form factor of thecomputer or hand held device. Finally, the usual constraints of lowcost, low power consumption and high reliability must also be met.

Currently, there are two dominant solutions to the pointing deviceproblem in the laptop marketplace, the Synaptics capacitive TouchPad™and the IBM TrackPoint™. Other companies make versions of these deviceswith similar functionality. Both of these devices fall far short ofsatisfying the above requirements. The TrackPoint™ is a small buttonthat is typically placed in the center of the laptop keyboard. Thebutton may be moved in a manner analogous to a “joy stick” by applying alateral force to the top of the button with a finger. Unfortunately, thebutton can only move a small amount; hence, the displacement of thebutton cannot be mapped directly into a displacement in the cursorposition on the computer display. Instead, the button displacementcontrols the direction and speed with which the cursor moves. Theaccuracy with which a user can position the cursor using this type ofvelocity control is significantly less than that achieved with aconventional mouse. This limitation is particularly evident in tasksthat require small, precise movements such as drawing in a computergraphics program.

The TouchPad™ is a blank rectangular pad, two to four inches on a side,typically placed below the keyboard of most laptops. The device sensesthe position of a finger on the surface of the rectangle relative to theedges of the device. This sensing is accomplished by measuring thecapacitance changes introduced by a user finger on a series ofelectrodes beneath an insulating, low-friction material.

Like the TrackPoint™, the TouchPad™ also suffers from lack of precision.It is inherently difficult to measure the capacitive changes introducedby the user, who is at an unknown potential relative to the circuit.Furthermore, the contact area of the user's finger is relatively large.Hence, to provide an accurate measurement of the finger position, thedevice must determine some parameter such as the center of the contactarea between the finger and the pad. Unfortunately, the contact areavaries in size and shape with the pressure applied by the user. Suchdeterminations are, at best, therefore, of limited precision. Inpractice, users are unable to repeatably execute precise movements.

There are also difficulties arising from false signals when the userinadvertently touches the pad with a finger or a wrist. In some devices,the “clicking” function of a conventional mouse is implemented bytapping on the pad. As a result, such inadvertent activation duringtyping causes the cursor to jump to a new location in the middle of thetyping operation and the text being inserted at the new location.

In previously filed U.S. patent application Ser. No. 10/723,957, whichis hereby incorporated by reference, a pointing device that meets theserequirements is described. The pointing device utilizes a puck thatmoves in a defined field of motion when a user applies pressure to thepuck via the user's finger. When the user releases the puck, a set ofsprings returns the puck to its centered position within the field ofmotion. The position of the puck and the pressure on the puck aredetermined by electrodes in the device. The position information is usedto position a cursor on the display screen. Software on the attacheddevice translates the motion of the puck during the time the user'sfinger is pressing on the puck into the appropriate cursor motion on thedevice's display. When the user releases the puck, the coupling betweenthe puck and the cursor position is broken by the software, and hence,the cursor does not move backwards while the puck is being recentered.

While the device taught in the above-described patent applicationprovides significant advantages over the dominant prior art solutions tothe pointing device problem in the laptop marketplace, there are anumber of areas in which improvements would be useful. In particular,this puck-based pointing device would benefit from the inclusion ofadditional input functions that provide the functionality of the scrollwheels discussed above.

SUMMARY OF THE INVENTION

The present invention includes a pointing device having a first surfaceon which a puck field of motion is defined, a moveable puck, and aposition detector. The moveable puck is confined to move on the firstsurface within the puck field of motion. The position detectordetermines a position of the puck in the puck field of motion and anangle of rotation of the puck about an axis perpendicular to the firstsurface. In one embodiment, the puck includes a puck electrode on asecond surface on the puck that is parallel to the first surface. Thefirst surface includes first, second, and third sense electrodes thatare parallel to the puck electrode, the puck electrode overlying aportion of each of the first, second, and third sense electrodes. In oneembodiment, the position detector includes a circuit for measuring thecapacitance between the puck electrode and each of the first, second,and third electrodes. In one embodiment, the puck electrode includes aplanar layer of conducting material having a shape that is notrotationally symmetric about any axis through the puck and perpendicularto the first surface. In one embodiment, the puck electrode includes aplanar layer of conducting material having a shape that is circularlysymmetric about an axis perpendicular to the planar layer, and theplanar layer is divided into first and second sections that areseparated from one another, at least one of said sections beingasymmetric. For example, the first section is not circularly symmetricabout the axis. In one embodiment, a finger sensing electrode isincluded in the puck. The finger sensing electrode includes a conductinglayer overlying the puck electrode and is moveable with respect thereto.The position detector includes a circuit for measuring the capacitancesbetween the puck electrode and each of the finger sensing electrode, thefirst electrode, the second electrode, and the third electrode.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top view of pointing device 10.

FIG. 2 is a cross-sectional view of pointing device 10 through line 2-2shown in FIG. 1.

FIG. 3 is a top view of a portion of the surface shown in FIG. 1 overwhich the puck moves in one embodiment of the present invention.

FIG. 4 is a schematic drawing of an equivalent circuit for electrodes51-55.

FIG. 5 illustrates an arrangement where the electrode arrangement isintentionally asymmetric to provide a measurement of the puck rotation.

FIG. 6 is a cross-sectional view of the pointing device such as thatshown in FIG. 5 through line 6-6.

FIG. 7 is a schematic drawing of a circuit for measuring the variouscapacitances.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

The manner in which the present invention provides its advantages can bemore easily understood with reference to FIGS. 1 and 2, which illustratea pointing device 10 according to one embodiment of the invention taughtin the above-described patent application. FIG. 1 is a top view ofpointing device 10, and FIG. 2 is a cross-sectional view of pointingdevice 10 through line 2-2 shown in FIG. 1. Pointing device 10 includesa puck 11 that moves over a surface 12 of a substrate 15 within a puckfield of motion 19 in response to a lateral force applied to puck 11.The force is typically applied to puck 11 by a user's finger. Puck 11includes a pressure sensing mechanism that measures the verticalpressure applied to puck 11. When the sensed pressure exceeds apredetermined threshold, the cursor tracking function is activated andthe cursor moves on the screen in a direction and distance determined bythe motion of the puck. In addition, pointing device 10 includes asensing mechanism for determining the position of puck 11 on surface 12.

When the user releases puck 11 by removing the user's finger 16, puck 11is returned to its centered position by the springs shown at 13 thatconnect the puck to the side 14 of the puck field of motion. Since theuser's finger is not applying a vertical force to puck 11 during itsreturn, the change in position associated with that return motion is notreported to the host device. That is, the cursor remains at its previouslocation. This provides a convenient “re-centering” capability,typically achieved on a mouse by lifting and replacing the mouse at thecenter of the field of motion. Re-centering is particularly necessary inlaptop computers, hand-held devices and other miniature applications inwhich the field of motion is constrained.

The above-described patent application teaches a number of mechanismsfor measuring the pressure exerted by the user on the puck, and hence,these mechanisms will not be discussed in detail here. For the purposesof this discussion, it is sufficient to note that a puck having a topsurface that can move relative to the bottom surface can be utilized.The top surface is held in place by a spring mechanism. When the userapplies pressure to the top surface, the top surface moves toward thebottom surface by an amount that depends on the applied pressure. Thedistance between the top and bottom surfaces of the puck is measuredutilizing one of a number of methods. For example, the top and bottomsurfaces of the puck can include conducting layers that form a parallelplate capacitor. The capacitance of this capacitor depends on thedistance between the plates, and hence, a measurement of the capacitanceprovides a measurement of the pressure applied by the user.

The manner in which the position of the puck is sensed in one embodimentis described in detail in the above-identified patent application, andhence, will not be discussed in detail here. For the purposes of thisdiscussion, it will be assumed that a capacitive sensing scheme can beutilized to determine the puck's position. Such a scheme is illustratedin FIG. 3, which is a top view of a portion of surface 12 shown in FIG.1 over which the puck moves in one embodiment of the present invention.Surface 50 includes four electrodes shown at 51-54 having terminals thatare connected to an external circuit. To simplify the drawing, theseterminals have been omitted. The puck has a bottom surface that includesan electrode 55 that is shown in phantom in the drawing. Electrodes51-55 are electrically isolated from one another. For example, electrode55 can be covered with a layer of dielectric that provides the requiredinsulation while still allowing electrode 55 to slide over the otherelectrodes. The electrodes can in fact be patterned on the back of thesubstrate whose surface is shown at 50. This reduces the capacitancebetween the electrodes and the puck electrode, but can be practical forsubstrate thicknesses of a few millimeters or less. The overlap betweenelectrode 55 and each of electrodes 51-54 depends on the position of thepuck relative to electrodes 51-54. Denote the overlaps between electrode55 and electrodes 51-54 by A-D, respectively.

Refer now to FIG. 4, which is a schematic drawing of an equivalentcircuit for electrodes 51-55. The portion of electrode 55 that overlapselectrode 51 forms a parallel plate capacitor having a capacitance thatis proportional to overlap A. Similarly, the portion of electrode 55that overlaps electrode 52 forms a parallel plate capacitor that has acapacitance that is proportional to overlap B, and so on. Since all ofthe capacitors share portions of electrode 55, the equivalent circuitconsists of four capacitors connected to a common electrode shown at 58.This electrode is just electrode 55. Hence, by measuring the capacitancebetween electrode 55 and each of electrodes 51-54, the position ofelectrode 55 relative to electrodes 51-54 can be determined. Thisdetermination can be made by a controller 59, which may be part of thepointing device or part of the host device of which the pointing deviceforms a part.

In the embodiments discussed above, the electrode on the bottom of thepuck is preferably circular in shape to reduce errors arising from theshape of the electrode. The restoring springs allow the puck to rotatesomewhat. If the user's finger is not centered on the puck during themotion of the puck, the resultant torque can cause the puck to rotateslightly. If the puck electrode is circularly symmetric, such rotationswill not alter the position measurement. If, on the other hand, the puckelectrode is not circularly symmetric, the degree of overlap between thepuck and the various electrodes will be different for differentrotations, even though the center of the puck is at the same location ineach case.

The present invention is based on the observation that such asymmetricelectrode designs can be used to measure the orientation of the puck,which can be useful information for cursor control or additionalfunctions. For example, the puck rotation can be measured and used toimplement an additional function such as scrolling. The rotation of thepuck in gaming actions can be used to rotate an object in the game. Forexample, in a game in which an army tank moves about a field of battle,the puck rotation can be used to control the direction of the turret onthe tank.

To provide a measurement of the puck rotation, the electrode arrangementis intentionally asymmetric. Refer now to FIG. 5, which illustrates onesuch arrangement. Pointing device 60 includes 4 electrodes 51-54 thatare located on the bottom of the field of motion 61. The puck electrodeis divided vertically into two halves shown at 65 and 66. Thecapacitance between each of the electrodes on the surface and each ofthe puck electrodes is then measured. Both the position and rotation canbe computed from these capacitance measurements. The rotationinformation can then be used to implement scrolling or some otherfeature.

As noted above, some puck rotation can occur during the normal motion ofthe puck. If this is a problem, the rotational information can berestricted to rotations that occur when the puck is at or near itsresting position. In this regard, it should be noted that the returnsprings will also return the puck to a predetermined orientation.

In one embodiment of the present invention, the two halves of the puckelectrode are designed such that the electrode obtained by electricallyconnecting the halves has a rotationally symmetric shape. In this case,the circuit arrangement shown in FIG. 3 can be utilized to determine thepuck position by electrically connecting the halves during the positionmeasurement. The same measurements can be repeated first with one halfdisconnected and then with the other half disconnected to provide therotational information.

The above-described embodiments utilized a puck electrode that was splitinto two portions. However, other electrode designs can be utilized. Thecapacitive measurements may be viewed as providing the area of the puckelectrode that overlaps each of the sense electrodes in the field ofmotion. These overlap measurements must provide the displacement of thepuck from some point of reference and the rotation of the puck about anaxis on the puck. For simplicity, the displacement will be specified inCartesian coordinates (x,y), and the rotation angle will be specified byA. Accordingly, there must be at least three sense electrodes. Inaddition, the electrodes shape and position must be such that both the xand y displacements can be determined. For example, if all of theelectrodes have the same shape and are aligned on a line in thex-direction, the y displacement could not be determined.

The shape of the puck electrode preferably satisfies two conditions ifeach possible position and rotation is to be detectable. First, theshape of the electrode must not be circularly symmetric about any axisin the field of motion. If this condition is not met, there may be a (x,y, A) set of values that provides the same overlap values as another (x,y, A) set. In addition, the puck electrode must overlap all of the senseelectrodes for each possible puck location and rotation. In embodimentsin which the puck electrode is small compared to the field of motion,more than three sense electrodes may be used to cover the surface of thefield of motion. In such embodiments, it is sufficient that the puckelectrode overlaps three of these electrodes, provided these threeelectrodes are not arranged in a straight line. If these conditions arenot met, operable pointing devices can still be constructed; however,the pointing devices may produce erroneous results at some locations.

As noted above, the pressure on the top surface of the puck is used todetect the presence of the user's finger and to simulate a “clicking”operation analogous to that used in a conventional mouse to signal theprogram that the present location of the cursor controlled by the puckis to be used for some function. For example, the click is used tosignal the data processing system that the item of a list on the screento which the cursor is now pointing should be selected. It should benoted that the same capacitive measuring system discussed above fordetermining the position and rotation of the puck can also be used tomeasure the pressure exerted by the user on the puck.

Refer now to FIG. 6, which is a cross-sectional view of the pointingdevice such as that shown in FIG. 5 through line 6-6. Pointing device 80utilizes a puck 81 having a top electrode 82 suspended on springs 84above the bottom surface of puck 81 on which electrodes 65 and 66 arelocated. In this embodiment, electrode 82 is prevented from leaving puck81 by flange 83 in the outer shell 85 of puck 81. When the user pusheson electrode 82, electrode 82 moves toward electrodes 65 and 66 adistance that depends on the force applied to electrode 82. Hence, thedistance between electrode 82 and electrode 65 or 66 provides a measureof the applied force. This distance is determined by measuring thecapacitance of a capacitor formed by electrode 82 and one or both ofelectrodes 65 and 66.

As noted above, the position of puck 81 in the field of motion and therotation of puck 81 can also be determined by measuring capacitances. Inthis case, the capacitances are those between electrodes 65 and 66 andelectrodes 51-54. Refer now to FIG. 7, which is a schematic drawing of acircuit for measuring the various capacitances. It should be noted thatelectrodes 65 and 66 can be connected separately to the input of op-amp92 or together, depending on the particular capacitance that is beingmeasured. The particular one of these electrodes that is connected tothe op-amp is determined by controller 93 via multiplexer 96. Tosimplify the drawing, the particular connections from the controller tothe multiplexer and the electrodes have been omitted. For the purpose ofthis discussion, it will be assumed that electrode 65 is connected. Whenreset switch 95 is first closed, sense electrode 65 and the outputvoltage V_(OUT) are forced to the potential V_(REF). After the resetswitch is reopened, a drive voltage V₁ is applied to one of electrodes51-54, 65, or 82 by controller 93. Consider a measurement on electrode51. Charge will develop across the relevant capacitor according toQ₁=C₁·(V₁−V_(REF)), where C₁ is the capacitance of the capacitor formedby electrode 65 and electrode 51. Since no charge can move onto or offof the sense electrode 65, the op-amp will apply a voltage acrossfeedback capacitor 94 to keep electrode 65 at potential V_(REF). ThusV_(OUT)−V_(REF)=C₁/C_(REF)·(V_(REF)−V₁), where C_(REF) is thecapacitance of capacitor 91. By sequentially making such measurements oneach of the driven electrodes, the position of the puck, the rotationalangle of the puck, and the pressure being applied to the finger sensorcan be ascertained. This circuit is advantageous for this applicationbecause it allows numerous capacitance measurements to be made using asingle op-amp and simple digital drive signals.

The signals derived for the location and rotation are then forwarded tothe data processing system 97 attached to the pointing device to controlthe location of cursor 102 and/or other features on display 98 attachedto the data processor. For example, the angle of rotation can be used torotate a selected object such as object 99 displayed on the display orto operate the scroll bar 101 on a window 100 shown on the display.

Various modifications to the present invention will become apparent tothose skilled in the art from the foregoing description and accompanyingdrawings. Accordingly, the present invention is to be limited solely bythe scope of the following claims.

1. A pointing device, comprising: a first surface having a puck field ofmotion defined thereon; a moveable puck confined to move on said firstsurface; and a position detector that determines a position of said puckin said puck field of motion and an angle of rotation of said puck aboutan axis perpendicular to said surface, wherein said puck comprises apuck electrode on a second surface on said puck that is parallel to saidfirst surface, wherein said first surface comprises first, second, andthird sense electrodes that are parallel to said puck electrode, saidpuck electrode overlying a portion of each of said first, second, andthird sense electrodes, and wherein said puck electrode comprises aplanar layer of conducting material having a shape that is circularlysymmetric about an axis perpendicular to said planar layer, said planarlayer being divided into first and second sections that are separatedfrom one another.
 2. The pointing device of claim 1 wherein said firstsection is not circularly symmetric about said axis.
 3. A pointingdevice, comprising: a first surface having a puck field of motiondefined thereon; a moveable puck confined to move on said first surface;and a position detector that determines a position of said puck in saidpuck field of motion and an angle of rotation of said puck about an axisperpendicular to said surface, wherein said puck comprises a puckelectrode on a second surface on said puck that is parallel to saidfirst surface, wherein said first surface comprises first, second, andthird sense electrodes that are parallel to said puck electrode, saidpuck electrode overlying a portion of each of said first, second, andthird sense electrodes, said puck further comprising a top electrodecomprising a conducting layer overlying said puck electrode and beingmoveable with respect thereto, and wherein said position detectorcomprises a circuit for measuring the capacitances between said puckelectrode and each of said top electrode, said first sense electrode,said sense second electrode, and said sense third electrode.